Short Answer
To protect sensor cables from EMI, use proper shielding, grounding, cable routing, and filtering techniques. These steps help prevent electrical noise from interfering with your sensor signal and ensure accurate, stable measurements.
Why EMI Matters for Sensor Signals
Electromagnetic interference (EMI) is unwanted electrical noise generated by nearby equipment such as motors, variable frequency drives (VFDs), power lines, and switching electronics.
Sensor signals—especially low-level analog outputs—can be affected by EMI, leading to:
- Signal noise or instability
- Reduced accuracy
- Intermittent or erratic readings
This is particularly important for precision devices like LVDTs, LVITs, and other position or temperature sensors.
Best Practices for Protecting Sensor Cables
1. Use Shielded Cables
Shielded cable is your first line of defense.
- Use cables with a braided or foil shield
- The shield blocks external electromagnetic noise before it reaches the signal conductors
- For most applications, shielded twisted-pair cable is recommended
2. Ground the Shield Properly
Shielding only works if it is grounded correctly.
- Ground the shield at one end only (typically the control system or instrumentation end)
- Avoid grounding both ends unless specifically required—this can create ground loops
- Ensure the ground connection is low resistance and secure
3. Separate Signal and Power Wiring
Cable routing plays a major role in EMI exposure.
- Keep sensor cables physically separated from:
- Power cables
- Motor leads
- VFD output wiring
- If cables must cross, do so at a 90-degree angle to minimize coupling
4. Use Twisted Pair Conductors
Twisting the signal wires helps cancel out noise.
- Twisted pairs reduce the impact of electromagnetic fields
- Especially effective for differential signal inputs
5. Choose Differential Inputs When Possible
Differential signal measurement improves noise rejection.
- Many signal conditioners and control systems support differential inputs
- These systems measure the difference between two wires, rejecting common-mode noise
6. Keep Cable Lengths as Short as Practical
Longer cables act like antennas.
- Minimize cable length wherever possible
- Use proper cable types if long runs are required
7. Add Filtering or Signal Conditioning
In noisy environments, additional filtering may be necessary.
- Use signal conditioners with built-in filtering
- Add ferrite beads or chokes to suppress high-frequency noise
- Consider using 4–20 mA outputs for improved noise immunity over long distances
8. Use Proper Connectors and Terminations
Poor connections can introduce noise.
- Ensure connectors are tight and properly shielded
- Avoid exposed conductors or loose terminations
- Maintain continuity of the shield through connectors when possible
Special Considerations for Industrial Environments
In environments with heavy electrical noise—such as factories, power generation systems, or mobile equipment—multiple mitigation strategies are often required together.
For example:
- Shielded cable + proper grounding + routing separation
- Differential inputs + signal conditioning
Common Mistakes to Avoid
- Grounding the cable shield at both ends (causes ground loops)
- Running sensor cables alongside high-voltage power lines
- Using unshielded cable in high-noise environments
- Ignoring connector shielding and termination quality
Bottom Line
EMI can significantly impact sensor performance, but it can be effectively managed with the right cable selection, grounding, and installation practices.
By using shielded cables, proper grounding, careful routing, and appropriate signal conditioning, you can ensure reliable, noise-free sensor operation—even in electrically noisy environments.
If you’re working in a high-EMI environment and want to ensure optimal performance, the HGSI engineering team can help you select the right sensor configuration and cabling approach for your application.
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